HILLSBORO, Mo. (AP) - A Ste. Genevieve teen who drove around for hours smoking synthetic marijuana before blowing through a red light and killing a Festus couple was sentenced Monday to five years in prison.

Keith Buehler, 18, pleaded guilty in March to two counts of involuntary manslaughter and synthetic-drug possession in connection with the crash on June 20, 2012.

Jefferson County prosecutors on Jan. 8 of last year filed those charges against Buehler. A Missouri Highway Patrol team of crash investigators found that he was driving 81 mph to 90 mph in a 55-mph zone when he struck a Lexus carrying Raymond McLean, 75, and Carolyn McLean, 70, according to court documents.

â€śFive years doesnâ€™t seem long enough for murdering two people coming home from the grocery store,â€ť said their daughter, Donna McLean of Washington, D.C.

She and her sister, Robin Miles-McLean, also of Washington, and other family members asked Circuit Judge Gary Kramer to impose a 14-year sentence, the maximum allowed for the manslaughter charges.

They told of how Raymond and Carolyn McLean worked tirelessly for a food pantry and for their church. They described their devotion to family and their other passions â€” Raymond McLean loved singing in barbershop choruses, and his wife of more than 50 years was an avid painter.

The crash happened shortly before 11 a.m. The McLeans were southbound on the exit ramp from southbound Interstate 55 and were making a left turn onto U.S. Highway 6 1-67 when Buehler crashed into them with his Chevrolet pickup.

The McLeans had a green light, according to a probable cause statement. Buehler, who was westbound, had a red light.

The crash that killed the McLeans was one of four traffic-related incidents involving Buehler in little more than a year, according to court records. One occurred before the fatal wreck; two took place after it, but before he was charged in the McLeansâ€™ deaths.

He pleaded guilty to driving carelessly in Ste. Genevieve County for a Nov. 26, 2011, crash in which he drove off the road and into a creekbed, hurting himself and two passengers. He also pleaded guilty to drinking underage â€” he was arrested as he rode with a drunken driver on Aug. 2, 2012, in Perry County. Both were misdemeanors, and he was ordered to pay fines.

About a month before he was charged with the McLeansâ€™ deaths, he was a passenger in a car in which the driver told police he crashed as he reached over to calm down Buehler, who was arguing with other passengers, in Ste. Genevieve County, court records say.

â€śThis young man seems incapable of learning from his mistakes,â€ť said Robin Miles-McLean.

Buehler apologized to family and friends of the McLeans who attended the sentencing Monday, saying he regretted the bad decisions he had made and that he has changed for the better.

â€śWords cannot express my sorrow for what I have done,â€ť he said, his voice choking with tears.